Using the Weak Signal Propagation Reporter Network to
Estimate Suitability of Radio Propagation Conditions for other
Communication Modes

INTRODUCTION

The Weak Signal Propagation Reporter (WSPR) Network is
an open worldwide network of amateur radio stations
using the WSPR digital communication mode conceived by
Dr. Joseph Taylor, K1JT. The WSPR mode is designed
to probe potential radio propagation paths with
low-power transmissions. Each WSPR transmission
carries encoded the originating station's callsign,
Maidenhead grid locator, and transmitter power in dBm.
The WSPR
program1 can decode signals with a
signal to noise ratio (SNR) as low as -28 dB in a 2500
Hz bandwidth. Stations with a personal computer, a
single sideband transceiver and internet access can
automatically upload their reception reports to a
central database at http://wsprnet.org2
that includes lists of active stations, forums,
statistics and a mapping facility.

RELATING WSPR SPOT REPORTS TO
OTHER MODES

The WSPRnet.org database hosts a large and detailed,
instantly accessible repository of historic and real
time data on radio propagation conditions. These
data may be used, in theory, to estimate when current
conditions would support communication using other modes
based on the relative sensitivity of WSPR to those
modes.

Figure 1 lists some published signal to noise ratio
thresholds in a 2500 Hz bandwidth for various communication modes in current
use and the calculated transmitter power needed to
achieve equivalent communication with each mode under
the same propagation conditions.* For example, a
radio circuit that supports a 5 watt WSPR transmission
at threshold would theoretically require an effective 37
dB power increase, or 25,000 watts, to accomplish the
same communication using the single sideband (SSB) voice
mode.

APPLYING WSPR SPOT DATA TO
OTHER MODES

One criticism of the WSPR network data has been that it
cannot be used to indicate usable propagation conditions
for other modes. However, WSPR spot report data
may be used to estimate the probability of communication
over a particular circuit when these data are normalized
for station transmitter power, antenna gain and the
relative sensitivities of alternative modes. The
following formula estimates the signal strength above
threshold for other communication modes based on WSPR
spot report data between two stations (all units in dB
and dBm).

Mark Hughes, GM4ISM, has written and published macro
code in a
Microsoft Excel spreadsheet3 that
retrieves a user specified subset of data from the
WSPRnet.org online database. I
have added calculations to this spreadsheet4
that tabulate and display the expected signal strengths
above threshold for the various communication modes over
the paths for each WSPR spot report. Note: This
Microsoft Excel spreadsheet requires support for
Visual Basic macros and may not work with Excel
program clones.

The desired WSPR spot report data is initially
retrieved by clicking on the "Get Web data" button on
the "GetWSPR" worksheet. Clicking on the "Ant
Gain/Power" button will allow the user to specify the
antenna gain in dB (relative to the WSPR station
antenna) and transmitter power in watts that will be
used for the data calculations. Clicking on the "Mode
Comp" button then transfers the WSPR report data to the
"dB over Threshold" worksheet and calculates and
displays the comparison data. Figure 2 shows these
calculations on some 7 MHz WSPR spot reports normalized
for a 5 watt transmitter power, and Figure 3 show those
reports normalized for 100 watt transmitter power.
Columns A through I contain the downloaded WSPRnet.org
data. Columns J through P contain the calculated
signal strength over threshold for each mode, with each
cell color highlighted through conditional
formatting. The spreadsheet cells that contain
values below the threshold that are not expected to
support communications are highlighted in red. The
values that are 6 dB (1 S unit) or higher above the
threshold are highlighted in green, and the intermediate
values are in yellow. The user may use the spreadsheet
menu controls to sort and filter the displayed data as
desired. By clicking on the "ReCalc" button, the user
can repeatedly input an alternative antenna gain in dB
(relative to the WSPR station antenna) and transmitter
power in watts into cells T1 and V1 (scrolled off the
screen) and display the calculations for the new
parameters on the worksheet.

The data presented in this manner facilitates
comparison of radio propagation conditions to stations
in the same and different regions of the world and shows
expected variations in signal strength over time and
some variations in reciprocity of reported signal
strengths over some paths. Sources for these
variations may include:

Non-reciprocal ionospheric propagation5

Variations in receiver sensitivity at each station

Variations in local noise level at each station

Variations in effective radiated power toward each
station due to antenna directivity

Figure 2. This chart shows expected signal strength in
decibels over threshold on these modes using a 5 watt
transmitter and a unity gain antenna.
Values below threshold are in red, above 6 dB in green
and intermediate in yellow.

Figure 3. This chart shows expected signal strength in
decibels over threshold on these modes using a 100 watt
transmitter and a unity gain antenna.
Values below threshold are in red, above 6 dB in green
and intermediate in yellow.

1. After entering the reported call,
spotter call and specifying the desired band in the blue
fields, a click on the gray gears in the Get Web Data box
retrieves the specified number of recent spots for this
radio circuit. To display (or change) the station
parameters for the comparison calculations, click on the
gray "Ant Gain/Power" button. The relative antenna gain
was specified as 0 dB (relative to the WSPR system
antenna) and the transmitter power as 50 watts in this example. This
screenshot was taken prior to clicking on the "Mode Comp"
button to display the following worksheet.

2. Here are the circuit calculations for a
relative antenna gain of 0 dB and 50 watts transmitter
power. Columns A through I contain the downloaded
WSPRnet.org data. Columns J through P contain the
calculated signal strength over threshold for each mode,
with each cell color highlighted through conditional
formatting. The values below the threshold that are not
expected to support communications are highlighted in red.
The values that are 6 dB (1 S unit) or higher above the
threshold are highlighted in green, and the intermediate
values are in yellow.

3. Click on the grey "ReCalc" button to
estimate circuit performance with alternative power and
relative antenna gain figures. Here is the estimated
circuit performance for 250 watts transmitter power and a
13 dB increase in antenna gain. The "ReCalc" button may be
used repeatedly to view calculations for different system
parameters.

4. The comparison modes and their
respective thresholds can be specified otherwise on the
"Constants" worksheet. This sheet also displays statistics
for each downloaded data set.